The patellofemoral joint presents a complex challenge to surgeons. Patellofemoral dysfunction (instability or pain) is often a result of an abnormal, lateral position of the tibial tuberosity. One method of treating patellar problems is tibial tuberosity osteotomy, wherein the tuberosity is moved to allow treatment of patellar pain and/or instability.
The assumption that the original tuberosity position is abnormal or suboptimal for distributing force is the reason for moving the tuberosity to a new position. Anteromedialization (AMZ) of the tuberosity is typically achieved by an oblique cut between the sagittal and coronal planes of the tuberosity. The obliquity can be altered to achieve the same degree of elevation with various degrees of medialization (the steeper the cut, the less the medialization). The desired slope of the osteotomy is determined preoperatively. The AMZ procedure begins by lateral release of subcutaneous tissues along the patellar tendon. A guide is used to position the tuberosity pin perpendicular to the posterior wall of the tibia. A horizontal guide, with a predetermined angle, is placed over the tuberosity pin. A cutting block is attached to the horizontal guide on the medial aspect of the tuberosity. The horizontal guide and cutting guide are adjusted so that the position of the cutting block is medial to the tuberosity in a posteromedial to anteromedial orientation as it travels distally. The obliquity of the jig will allow the distal cut of the tuberosity to exit laterally, fully freeing the tuberosity.
Two breakaway pins are inserted into the tibia to help secure the cutting block. The angle of the slope is visualized as the slope selector outrigger-aiming device is temporarily applied to the block. The tip of the slope selector is placed posteriorly on the lateral face of the tibia (this predetermines where the osteotomy will exit).
Once the slope and planned cut exit have been determined, the cutting block is attached to the tibia with fixation pins (placed through holes in the cutting block) into drill holes in the tibia. A custom retractor is placed posterior to the tibia to protect deep neurovascular structures. An oblique cut is made from the proximal extent of the posterior cut to the lateral proximal attachment of the patellar tendon to the tuberosity. Once the tuberosity is fully released, and after the desired (final) tuberosity position is achieved, the newly-repositioned tuberosity is typically fixed by employing two interfragmentary screws.
Improved instrumentation and methods of quantifying the shift in the anterior and medial direction of the tibial tuberosity when performing the AMZ procedure are needed.